GuybrushFreepwood wrote:
My boss has solar panels and has a similar predicament. He says he's going to get a battery array so he can store the electricity. He's a proper miser, so he must have found a way to make it pay.

I don't suppose you could find out which battery setup he's going for?

Really struggling with the economics of the batteries I've looked at. At many thousands of pounds all in, even if they theoretically reduced the electricity bill to zero it would take ages before they paid for themselves, if ever considering they wear out.

Psiloc wrote:
Bought a house that has solar panels on the roof and I'm getting a bit obsessed with it. I've never been one to fuss over electricity bills but now there's a gadget involved I keep trying to think of ways to make the most of it. Problem is we both work all day and miss most of the sun.

I installed one of those solar diverters that puts any unused solar electricity into the immersion heater for free hot water but it only runs for about an hour before the tank is hot and the free energy is going to waste again.

Anyone else generating their own energy? How are you getting the most out of it?

Out of interest, how did you buy a house with panals on? We put in an offer on a house, and the bank declined it for the mortgage - something to do with a risk because they were leased.

Well interestingly I do know that the house we bought was previously sold STC and the buyer pulled out at the last minute due to problems with her mortgage. I do wonder whether it was due to the solar panels.

I think the concern is that the panels could have been installed by cowboys for all they know and could somehow ruin the house? Either that or the legalities of renting out your roof space, even though that's strictly your own business.

Unless you take the loss for batteries - you'd want to find something to use the free energy for, that saves/earns more money back than the investment in the equipment.

Elon Musk is working on the battery cost issue at the moment. If he can keep selling these cars, and not go out of business, he may well be able to drive that cost down significantly.

Batteries paired with supercapacitors will HOPEFULLY become the best bet in the next decade.

Apparently there was a relatively recent project in Morocco or nearby, that used focused heat from the sun to heat salt to an extremely high temperature, and used that heat at night to carry out some other job.

Is there anything like that, that'd work on a single home scale, using the free electricity as the power source?

Ryze wrote:
Unless you take the loss for batteries - you'd want to find something to use the free energy for, that saves/earns more money back than the investment in the equipment.

Elon Musk is working on the battery cost issue at the moment. If he can keep selling these cars, and not go out of business, he may well be able to drive that cost down significantly.

Batteries paired with supercapacitors will HOPEFULLY become the best bet in the next decade.

Apparently there was a relatively recent project in Morocco or nearby, that used focused heat from the sun to heat salt to an extremely high temperature, and used that heat at night to carry out some other job.

Is there anything like that, that'd work on a single home scale, using the free electricity as the power source?

Any geologists in the house?

Lots of people looking for funding to develop ideas, but I don't think there's a product on the market. I'm not sure I'd want a vat of molten salt on the property though.

Other phase-change ideas go the other way and turn air or nitrogen into liquid via cooling. Store that and use waste heat from elsewhere to combine with for a heat engine. No products though I think.

Yeah our mortgage people said it's considered stupid and bad form even within the industry not to lend because of solar panels. Unless they're aware of problems with the installation company or something I suppose.

I think the main issue might be them thinking they'd be unable to sell the property in the case of a repossession... because of other lenders having the same stupid policy

@GuybrushFreepwood Ping. Wouldn't mind knowing what battery your boss gave the nod if you ever spoke to him about it?

@Technoishmatt Yeah as far as I can tell you're looking at mid-four figures for any half decent battery. I'd love one for the convenience of not having to time-shift the heavy duty appliances or whatever, but I'm not certain it would save a load of money. Our house when it's just 'ticking over' in the evening even with the entertainment on uses about 350-400watts, so like 6 or 7p per hour. Obviously this would rocket if we switched on all the white goods but again if you're smart about it you can time all that to come on in the day.

I just don't see a battery paying for itself before it dies of old age. I struggled with the economics of the £200 Solar iBoost and a battery is quite the step up from that.

Gotta view it as pioneering tech I guess, it'll get better and more efficient surely?

Every other taxi driver in my town has a Prius now. It's happened all of a sudden.

The Prius is ideal for taxis. Constant stop-start driving, nothing could match it except full electric, and they are quite expensive still. I reckon there's a good plan for cheaper short-range electric taxis with charge-points at the taxi ranks. It'll probably take a zero-emission city-wide target to make it feasible though.

Charging an electric car would be a great way of making use of household solar as it happens. You can get charge points installed that, like the Solar iBoost (which is for hot water), only ever use surplus solar energy to charge your car without, in theory, ever drawing energy from the grid.

Of course you're going to need at least one full summer's day worth of uninterrupted sunlight to completely charge the battery up for free. You can program them with a time that the battery MUST be charged by so that it knows to use the grid if it's going to miss the target.

Again though usefulness is limited if you (and the car) aren't in during the day. I suppose depending on your commute you might be able to manage with it charging over the weekend and then seeing if that charge will carry you through the week?

Psiloc wrote:
Charging an electric car would be a great way of making use of household solar as it happens. You can get charge points installed that, like the Solar iBoost (which is for hot water), only ever use surplus solar energy to charge your car without, in theory, ever drawing energy from the grid.

Of course you're going to need at least one full summer's day worth of uninterrupted sunlight to completely charge the battery up for free. You can program them with a time that the battery MUST be charged by so that it knows to use the grid if it's going to miss the target.

Again though usefulness is limited if you (and the car) aren't in during the day. I suppose depending on your commute you might be able to manage with it charging over the weekend and then seeing if that charge will carry you through the week?

You can also use the car as a battery, at least that option exists in the Nissan Leaf (Car to the Grid, I think they call it). So in the event of a power cut you can run an isolated sub-circuit (you don't want to electrocute the workers doing the repairs).

I guess things might change again if as expected the government brings out new rules to make it possible to sell surplus day power to the grid, to replace the previous government subsidy.

Thing is... I can buy 100% renewable from the grid. Continuing to choose that option should encourage more investment in large scale renewable, which is more cost and carbon efficient than a mini grid is now

Psiloc wrote:
Charging an electric car would be a great way of making use of household solar as it happens. You can get charge points installed that, like the Solar iBoost (which is for hot water), only ever use surplus solar energy to charge your car without, in theory, ever drawing energy from the grid.

Of course you're going to need at least one full summer's day worth of uninterrupted sunlight to completely charge the battery up for free. You can program them with a time that the battery MUST be charged by so that it knows to use the grid if it's going to miss the target.

Again though usefulness is limited if you (and the car) aren't in during the day. I suppose depending on your commute you might be able to manage with it charging over the weekend and then seeing if that charge will carry you through the week?

You can also use the car as a battery, at least that option exists in the Nissan Leaf (Car to the Grid, I think they call it). So in the event of a power cut you can run an isolated sub-circuit (you don't want to electrocute the workers doing the repairs).

THIS.

Get an electric car that can charge in the day from the panels, and supply your house at night.

Have a look into it, but that wont help you to get to work unless you WFH, so...

I donít think youíre going to be able to charge a 100kW car battery with your solar panels, it would take a week.
I wonder if instead of charging a battery during daytime it would make economic sense to mine bitcoin. For the price of a battery pack you could get a shitload of gpus.

Fake_Blood wrote:
I donít think youíre going to be able to charge a 100kW car battery with your solar panels, it would take a week.
I wonder if instead of charging a battery during daytime it would make economic sense to mine bitcoin. For the price of a battery pack you could get a shitload of gpus.

Yeah that was mentioned on the last page. It's such a waste of energy though, I'm not looking forward to having to do that.

A plug-in hybrid would have a smaller battery, good for 50km or so, you could get that charged reasonably well on the weekend and burn less fuel all week.

gammonbanter wrote:
This thread is amazing! So, how big a panel would I need to just heat water in my immersion tank?

Also, where is a good place to start shopping, so much choice out there!

It seems if all that electricity is going to waste during the day, it might be only wise to generate enough for hot water.

Quick bit of research, I'd need to generate about 3KW and the would require 12 250w panels. Does this sound right EG?

That's a lot more than a water heater. You'd pretty much run a small house base load requirements on that (obviously a 3kW kettle will kick you well over) for the sunlight hours. You will need to divert the energy to the water system when you are over-supplying which is an extra cost. I think I have the name of a UK supplier somewhere but not on my phone.

If you're JUST interested in hot water, there are solar thermal systems that do just that and would take up less roof space. No idea how much they cost but I know they're pretty popular and are more efficient at the job. Using a solar PV (electric) system to power the immersion heater is like a bonus add-on, it's rarely the main focus when installing a system.

If you're interested in how the immersion heater thing works (they're called power diverters), let me quote my review for the Solar iBoost which is what I use.

I'll spoiler it as it's wordy:

So it's early days for me and our Solar iBoost but so far, I'm pretty impressed. Installation is pretty easy and for the most part self explanatory, you simply cut the wire to your immersion heater and splice the main unit in between. While the official line is that you need to get a qualified electrician in to do it for you, I did it myself and personally found it no more complicated than rewiring a couple of plugs. I'm not in any way advising you to do install this without the advice of an electrician - this is simply an anecdote.

The sender is a AA battery powered diddy that you clamp around the main live feed to your main electric meter. The sender wirelessly communicates with the main unit, telling it how much electricity you are currently exporting to the grid, and the iBoost fires the immersion heater at precisely this energy level. It then constantly monitors and adjusts the power based on the solar conditions, meaning your hot water is only ever powered by the solar energy that you would have otherwise wasted. It's a brilliant idea honestly, and well executed.

So why do you need this device rather than simply flicking on the immersion when it's sunny? It's simple - your immersion heater is probably rated to 3KW, and it's incredibly unlikely you'll consistently have in excess of 3KW solar power going spare, if ever. So if you were generating 2KW and had your immersion on, you were paying for the remaining 1KW of electricity from the grid. Even when the tank got to temperature because the thermostat kicked in, when the heater came back on to top up the temperature it would do this by firing at 3KW for a short period of time. So even though it was using very little electricity over time, the short bursts where it came on were still probably in excess of your solar input, meaning you would be paying for it.

This device is simply designed to manage this situation automatically, by only ever passing as much electricity to the immersion as would otherwise be exported. This means that you can continue to use all the solar energy you want throughout the house, and only the "spare" energy, when available, is diverted to the immersion. You really don't have to think about the device once it is installed - you just enjoy the free hot water.

Haven't paid for hot water since February. And even over the winter it would have helped with the bills by reducing the demand on the gas. Not bad considering it doesn't interfere at all with the other benefits you're of the solar. It just does what it can with the spare energy.

gammonbanter wrote:
This thread is amazing! So, how big a panel would I need to just heat water in my immersion tank?

Also, where is a good place to start shopping, so much choice out there!

It seems if all that electricity is going to waste during the day, it might be only wise to generate enough for hot water.

Quick bit of research, I'd need to generate about 3KW and the would require 12 250w panels. Does this sound right EG?

Just seen this. You've started from the immersion heater and worked backwards, which isn't right

12 panels generating 3KW sounds correct and would be a fine system, and immersion heaters would use 3KW under normal conditions (any appliance with an electric heating element is going to be the biggest draw on your house) but you can be much cleverer about it by installing a diverter as explained above.

As for what solar PV system to install, you'd probably be best getting a quote from a few people and simply installing the most panels you can afford and will fit on your roof. They WILL pay for themselves given enough time. You're probably likely to get a decent price on them right now.

Fake_Blood wrote:
I donít think youíre going to be able to charge a 100kW car battery with your solar panels, it would take a week.
I wonder if instead of charging a battery during daytime it would make economic sense to mine bitcoin. For the price of a battery pack you could get a shitload of gpus.

Heh, from empty, you're not wrong. But I'm fairly confident I could do a lot of my commuting on solar if it was left charging over the weekend in the daylight. In practice there's definitely going to be some reliance on the grid, but that's not to be sniffed at.

gammonbanter wrote:
This thread is amazing! So, how big a panel would I need to just heat water in my immersion tank?

Also, where is a good place to start shopping, so much choice out there!

It seems if all that electricity is going to waste during the day, it might be only wise to generate enough for hot water.

Quick bit of research, I'd need to generate about 3KW and the would require 12 250w panels. Does this sound right EG?

Just seen this. You've started from the immersion heater and worked backwards, which isn't right

12 panels generating 3KW sounds correct and would be a fine system, and immersion heaters would use 3KW under normal conditions (any appliance with an electric heating element is going to be the biggest draw on your house) but you can be much cleverer about it by installing a diverter as explained above.

As for what solar PV system to install, you'd probably be best getting a quote from a few people and simply installing the most panels you can afford and will fit on your roof. They WILL pay for themselves given enough time. You're probably likely to get a decent price on them right now.

I'm assuming you've got a roughly south facing roof etc.?

Yep, south facing roof available! Can I expect any panels I install to last 25 years? You have to imagine that they'll be cheap as anything by then?

Yep I've read somewhere that they're expected to retain over 80% of their efficiency after 25 years, or something like that.

In terms of how long they literally remain in working order I don't know, but I think you're more likely to eventually upgrade them to whatever future tech is available rather than replace them because they die.

EDIT: If you go for this by the way you should consider switching energy providers to one that pays you for energy that you export. I know Octopus do this. It's still always more economical to use all the energy you can, but it's a pretty nice bonus.